It's a very tough question to answer. Based on my personal experience:
The NT1 performs really well out on the track and is very easy to drive well. As with the MTX-4 (w/front diff), the NT1 was setup right out of the box for the track I race on. If you can deal with some of it's "quirks", it's a great car.
The RRR is a very good "overall" car. It take a little more time and effort to find the right setup based on the track you race on and your driving style, but it only has a few mechanical issues that are easy to deal with.